U.S. Patent 4,508,842 discloses a highly active vanadium-containing catalyst capable of producing ethylene polymers having a broad molecular weight distribution. Said catalyst comprises:
(A) a solid catalyst precursor consisting essentially of
(1) an inorganic carrier, as support for PA2 (2) the reaction product of (a) a vanadium trihalide and (b) an electron donor, and PA2 (3) a boron halide or alkyl aluminum modifier, PA2 (1) a solid, particulate, porous, inorganic carrier, as support for PA2 (2) the reaction product of PA2 (3) a boron halide or alkyl-aluminum modifier, PA2 (1) a solid, particulate, porous, inorganic carrier, as support for PA2 (2) the reaction product of (a) a vanadium trihalide and (b) an electron donor, PA2 (3) a boron halide or alkyl-aluminum modifier, and PA2 (4) an oxygen containing molecular weight distribution (MWD) regulator having the formula A--R--B or R.sup.l --B , wherein A, R, B and R.sup.l are as defined above,
(B) an alkylalum-inum cocatalyst, and
(C) a halohydrocarbon polymerization promoter.
The polymers produced in accordance with U.S. Pat. No. 4,508,842 have a relatively broad molecular weight distribution, and excellent extrudability. These properties render them extremely useful in a wide variety of applications, such as wire and cable insulation, blow molding, film, and pipe fabrication. However, such polymers cannot be used in other applications, such as injection molding, which require a narrower molecular weight distribution. U.S. Pat. No. 4,434,242, on the other hand, discloses vanadium containing catalyst compositions useful in the preparation of ethylene polymers a narrow molecular weight distribution. Such compositions are obtained by:
(1) drying an inorganic oxide having surface hydroxyl groups to form a support substantially free of adsorbed water,
(2) reacting the surface hydroxyl groups of the support with an organometallic compound,
(3) reacting the support treated in this manner with a tetravalent or pentavalent vanadium compound, and
(4) reacting the product of step (3) with an ether-alcohol.
While the catalyst compositions prepared in this manner have been found useful in the preparation of polymers having a narrow molecular weight distribution, the presence of ether-alcohols in such compositions has been found to adversely affect polymer productivity.
U.S. Pat. No. 4,435,518 discloses catalyst compositions similar to those of U.S. Pat. No. 4,434,242 except that the ether-alcohol of the latter patent is replaced with a monofunctional alcohol. Again, while such compositions are useful in the production of polymers having a narrow molecular weight distribution, the presence of alcohol in such compositions adversely affects polymer productivity.
The use of difunctional alcohols in place of monofunctional alcohols has been suggested in U.S. Pat. No. 4,435,519. However, such substitution has not been found to consistently narrow the molecular weight distribution of the polymers.